Medical X-ray films typically comprise a transparent substrate coated on one or both sides with a light sensitive silver halide emulsion. Exposure is effected by means of fluorescent screens placed in contact with the emulsion-coated side(s) of the film. The screens absorb a proportion of the X-rays impinging on them and re-emit the energy as visible light, normally in the green portion of the spectrum, and the emulsions are sensitised accordingly. Laminar grain emulsions are increasingly used for X-ray films because of their ability to reduce crossover, i.e. the exposure of an emulsion on one side of the base by light emitted by the screen on the other side of the base. Although crossover decreases the overall exposure required to achieve a given Dmax, it degrades significantly the image resolution. Laminar emulsions have the desirable properties of reducing crossover without undue loss of speed. Even in the case of single-sided X-ray films, laminar emulsions are preferred because they enable the use of reduced amounts of silver. Dye-containing underlayers situated between the base and the emulsions are also frequently used to reduce crossover and halation in double-sided films. In single-sided films, an antihalation layer is normally coated on the back. Protective layers, e.g. of hardened gelatin, are normally coated on top of the emulsions to improve the durability of the film.
The exposed films are typically processed by immersion in warm (about 35.degree. C.) alkaline developer solution containing developing agents e.g. hydroquinone, phenidone etc., stabiliser e.g. sulphite ion, antifoggants and a hardener e.g. a dialdehyde, such as, glutaraldehyde. Thereafter, the film is fixed, washed and dried, the entire process taking in the region of 90 to 110 seconds dry-to-dry, or longer. There is increasing interest in reducing this time to less than 60 seconds, preferably less than 45 seconds, in the interests of improved productivity, especially during mass screenings. Possible means for reducing the processing time include the use of more concentrated developer solutions and/or higher temperatures, both of which are undesirable from an environmental point of view.
The incorporation of developing agents into photographic elements is disclosed widely in the literature. In most cases the developers are incorporated in the emulsion layer itself, but the possibility of incorporation in an adjacent layer is often mentioned. The bulk of the prior art relating to incorporated developers is directed to graphic arts films and plates involving high-chloride non-laminar-grain emulsions, with the object of reducing the amount of noxious chemicals the user must handle before, during and after the processing stage. Also, by using an activator, rather than a developer as the processing solution, replenishment/replacement during continuous operation is less critical.
JP01-072141 and U.S. Pat. No. 5,028,520 disclose photographic elements comprising a laminar silver halide emulsion and a polyhydroxybenzene incorporated in the emulsion or in an associated hydrophillic colloid layer. U.S. Pat. No. 5,028,520 relates specifically to X-ray film. The Japanese application specifies a maximum concentration of 0.1 mole/mole Ag for the polyhydroxybenzene and claims a reduction in stress-sensitivity, while the U.S. patent specifies a concentration in the range 0.03 to 0.50 moles/mole Ag and claims a reduction in reflectivity of the developed silver image. The preferred concentration range disclosed is 0.03 to 0.30 moles/mole Ag, and most preferred 0.05 to 0.10. Processing is by conventional developer solutions. In both cases, the formula for the polyhydroxybenzenes encompasses compounds such as resorcinols. There is no disclosure of the presence of auxiliary developers, such as phenidone, in the films.
It has now been found that the use of incorporated developing agents, present in a layer separate from the emulsion, in an X-ray film having a laminar grain silver halide emulsion, enables rapid processing in simple activator solution. Surprisingly, this is achieved without detriment to the sensitometry of the film.